1. Field of the Invention
The present invention relates in general to passive restraint airbag systems. In particular, the present invention relates to an improved hybrid inflator for airbag systems providing adaptive performance.
2. Description of the Related Art
In airbag systems there is typically a cushion which, upon a collision, is inflated to provide protective cushioning to the passenger. To inflate the cushion such systems employ an inflator to produce a quantity of inflation gas. Various inflators operating upon different principles are known. For each operating principle, there is a slight difference in performance such as the rise and fall of pressure in the cushion over time. As such, for different applications, inflators operating on different principles are preferred.
One known class of inflator is referred to as hybrid. In hybrid inflators, there is a pressure vessel containing a quantity of pressurized inert gas. To fill a cushion simply with stored gas would required a large quantity of the gas, resulting in a large inflator. To reduce size and weight, hybrid inflators exploit the principle that the pressure of a gas increases with temperature. Therefore, hybrid inflators include various types of heaters which heat the gas before it is released from the inflator. This permits a lesser quantity of gas to be stored, greatly reducing inflator size.
Even with this size reduction, hybrid inflators have typically been rather large. As such, they have typically been used for passenger protection, where relatively large spaces are available behind the vehicle dashboard to store the inflator. Providing a hybrid inflator which is sufficiently small to be mounted to a steering wheel for driver side protection has been more difficult.
Additionally, there has been a growing desire to provide adaptive airbag systems. Adaptive systems tailor airbag performance to various criteria, such as ambient temperature (which affects gas pressure as noted above), severity of the collision, position of the passenger, etc. As an example, an adaptive airbag system could sense whether the collision is moderate or serious. If the collision is moderate, a lesser quantity of gas is used to inflate the cushion. If the collision is serious, a greater quantity of gas is used, providing a "harder" cushion to provide the increased protection required.
While such adaptive systems are desirable, they typically require additional components on the inflator, increasing its size. As such it has been even more difficult to provide an adaptive hybrid inflator which will meet the size requirements for vehicles, especially for driver side applications.